1. Field of the Invention
The present invention relates generally to wireless optical communication, and more particularly to an optical receiver for wireless optical communication.
2. Description of the Related Art
Recently, the luminous efficiency of Light Emitting Diodes (LEDs) has improved while the unit price of LEDs has dropped. Accordingly, LEDs are being used not only in handheld devices, displays, automobile illuminations, advertising boards, sign boards and the like, but also in fluorescent and incandescent electric lamps. As compared to fluorescent and incandescent lamps, LEDs are capable of emitting light for a substantially longer period of time while using lower electric power.
Interest in optical wireless technology that is complementary with Radio Frequency (RF) technology has increased due to the limitations of RF technology, such as the exhaustion of frequencies in the RF band and the likelihood of crosstalk among wireless communications, the increase of the security requirements for wireless communications, and the advent of the very high speed ubiquitous communication environment of fourth generation mobile communication (4G) wireless technology. As an alternative measure for RF communication technology, various studies and developments are being performed on visible light wireless communications using LEDs.
For portable devices such as mobile phones and Personal Digital Assistants (PDAs), and small household electric products such as digital cameras and Motion Picture Experts Group (MPEG) Layer Audio 3 (MP3) players, extensive research has been performed for peripheral interfaces enabling inter-device communication by providing an Infrared Data Association (IrDA) module-based infrared ray. In addition, products related to such interfaces are now commercially available. Bluetooth® and Zigbee® are examples of such products that do not cause crosstalk among infrared wireless communication devices unlike RF communication, and promote increased communication security and low power of operation.
There has been recent discussion on the use of inter-device wireless communications using LEDs or Laser Diodes (LDs), which are very advantageous in terms of technology and price as compared to IrDA modules. If visible light LEDs or LDs are employed in peripheral interface communication, a user can visually confirm communication paths, which enables visual confirmation of communication security. In addition, since it is easy to align communication paths, the diffusion angle can be minimized, whereby high speed communication or low power designs can be implemented.
In a wireless optical communication including visible light communication, a receiver should have a wide light concentration area and a wide view angle. In particular, if the diffusion angle of light is small in visible light communication, the arrangement of a communication link can be more easily performed as the light concentration area of the receiver is increased. A conventional light concentrator employing an optical lens is formed in a three dimensional shape having a wide light concentration area, but also has an increased volume which compromises the application of such a light concentrator to small hand-held devices.
FIG. 1A illustrates an example in which the light concentration angle of a receiver 120 is narrow while the diffusion angle of a transmitter 110 is wide. In FIG. 1A, there is a limitation in the transmission distance and speed due to the large diffusion angle. If the light concentration angle of the receiver 120 is wide and the diffusion angle of the transmitter 110 is narrow as shown in FIG. 1B, the arrangement can be easily performed and long distance and high speed communication can be obtained.
In order to increase the light concentration efficiency in a narrow diffusion angle as shown in FIG. 1B, a light concentrator as shown in FIGS. 2A and 2B has been proposed. FIG. 2A illustrates a light concentrator, and FIG. 2B illustrates a cross-sectional view of the light concentrator, in which a light incident path of an optical signal is schematically depicted.
Because the light concentrator shown in FIGS. 2A and 2B is three-dimensionally shaped, it exhibits an increased receiving rate within a limited diffusion angle range. Accordingly, it is difficult to apply the light concentrator in FIGS. 2A and 2B to a hand-held device.